This invention relates in general to the calibration of a data signal channel. More particularly, this invention relates to a fast closure method for use in calibrating a data signal channel such as the record/reproduce channel of a magnetic tape recorder. The method of the invention reduces the number of iterations required of the calibration procedure to bring the channel response within acceptable error limits.
A data signal channel, such as a record/reproduce channel of a magnetic tape recorder, must be calibrated (sometimes frequently) because of changes in the response of the channel due to changes in the characteristics of the components of the channel. Thus, in a record/reproduce channel of a magnetic tape recorder, the magnetic record and reproduce heads are subjected to wear through constant abrasion by magnetic tape, thus, changing the frequency response of the heads over time. Such changes in frequency response introduce frequency and phase distortion into a signal transmitted over the data signal channel. This distortion is undesirable since an ideal data signal channel should have minimal effect on a transmitted signal. Thus, it is desirable that the channel response be uniform.
In order to adjust for changes in channel response, it is customary to periodically calibrate the response of a data signal channel. Typically, the calibration procedure is effected by transmitting a known waveform signal over the channel and measuring the response of the channel to the known signal. Any distortion introduced by the channel into the signal, will result in a measured signal response which is different from the expected signal response. If the difference or error is not within acceptable limits, then control elements in the data signal channel are adjusted and the calibration procedure repeated. This procedure is reiterated until the channel response is brought within acceptable limits. It has been found that such a calibration procedure normally requires several iterations to effect a channel response which is acceptable. In a multispeed, multichannel magnetic tape recorder, effecting a calibration procedure for each channel, at each speed is a time-consuming task. For example, if the magnetic tape recorder is operable at eight different tape speeds and includes 20 data channels, the calibration procedure must be carried out 160 times. There is thus a need in the art for a method for effecting calibration of a data signal channel which is accurate, effective and fast.